Pilot-aided channel estimation for systems with virtual carriers

In this paper, we investigate various frequency-domain channel estimators for orthogonal frequency division multiplexing (OFDM) systems with virtual carriers (VCs). As conventional estimators cannot estimate the channel transfer function (CTF) at VCs, DFT-based estimators are not directly applicable in OFDM systems with VCs. To circumvent this, we present least squares (LS), generalized linear minimum mean square error (GLMMSE) and generalized singular value decomposition (GSVD) methods to estimate the CTF at VCs. Further, by exploiting the received data samples at VCs, we describe a novel noise variance estimation method. We also analyze the performance degradation due to estimated noise variance and the channel correlation mismatch. Performance comparison shows that the discrete Fourier transform (DFT)-based channel estimators incorporating the proposed CTF estimation at VCs achieve at least 6 dB gain when MMSE= 10-3 compared to frequency-domain LS estimator. Further, even though the DFT-based LS estimator with VCs performs worst among all the DFT-based estimators, it is the most robust estimator.